This invention relates to fire control systems for military applications and, more particularly, to such a system employing a beam steered laser to eliminate firing errors and increase accuracy.
Laser fire control systems are known in the art. See, for example, U.S. Pat. Nos. 3,904,163, 4,161,652, 4,213,700, 4,577,962, 4,665,795, 4,695,161, 4,787,291, and 4,876,942. It is also known to incorporate portions of fire control systems into goggles, helmets, or similar apparatus worn by a user of a fire control system. See, for example, U.S. Pat. No. 4,040,744. Of recent interest is a beam steered laser for fire control system which incorporates night vision goggles. In this system, a laser beam is steered to a point (or points) where the potential fall of a projectile will hit. Since the fire control system is mounted on some type of platform (tank, helicopter, boat, etc.) the system must take into account not only the ballistics of the projectile, but also platform motion. A gunner using this system performs a series of functions one of which includes range finding, and another of which is target designation. For this purpose, a laser is co-located with the gunner who operates the laser in a pulse mode, for example, for target ranging, and in a continuous wave (CW) mode for target designation. In operation, the gunner first performs target location and ranging operation. A system computer then computes a lead angle by which the firing unit must lead the target in order for the round to hit it. The gunner now uses this information to realign the laser and designate the target. At this time, the system is ready to fire a projectile at the designated target.
The system as outlined does have certain disadvantages. For example, the lead angle is not continuously recomputed. Therefore, any delay (latency) by the gunner in realignment of the laser and firing of a round may produce a firing error and a missed target. In addition, platform movement and vibration may make it difficult for the gunner to maintain the realigned beam on the designated target.
There are various approaches which may be undertaken to resolve the above noted problems. For example, an instrumented two axes, stabilized laser could be used as a reference for the gun. The gun and laser would be slaved together using either the gunner or an appropriate servo-system so necessary corrections are made before firing. In such a system, the laser would be vibration isolated and stabilized so as to provide a stable platform. Thus, a servo for the laser would require wideband capability to help compensate for stabilization errors and the platform would be stable for appropriate fire control pick-ups and would create a stable, spatial reference. There are three drawbacks to this approach. First, because the stabilization servo is a mechanical unit, it has a limited bandwidth. Second, again because the servo is mechanical, it is difficult to retain boresight because of vibrations (whether platform, gun firing, or both). Third, the usefulness of a mechanical servo in a high vibration environment for any prolonged period is questionable.
All of these limitations can be circumvented if a totally electronic beam steered laser having no mechanical parts is used. The steering of the laser away from the direction of the gun would compensate for ballistic corrections, kinematic corrections, and short duration rotational and translational movements of the platform on which the gun is mounted. This latter capability also facilitates the possibility of coincidence firing.